The invention is in the sector of packaging containers of incoherent material, generally containers of liquids for human consumption. Such containers are produced in continuous fashion from a tubular wrapper fed along a substantially vertical direction. The tubular wrapper is filled with incoherent material and subsequently sealed and cut along transversal seal lines which define the individual containers.
As is well known, the wrapper material, generally constituted by heat-sealable paper material, is continuously unwound from a reel towards a folding device adapted to join opposite longitudinal edges of the wrapper to each other. The tubular wrapper is then advanced along a vertical path through a filling unit. The filling unit delivers the incoherent material inside the tubular wrapper through an upper opening of the tubular wrapper. Downstream of the filling unit is a forming device provided with heated bars adapted to perform a series of seals, transverse to the longitudinal axis of the tubular wrapper. The heated bars are mounted on a fixed support structure and are movable only to approach each other. In this way, the container containing the incoherent material is defined between two consecutive seal lines. Lastly, a cutting member positioned downstream of the forming device separates the containers from each other by a transverse cut along the seal line.
The known packaging units described above have important drawbacks, which are linked mainly to the forming device.
It should be noted that the heated bars are positioned at opposite sides of the tubular wrapper and movable to approach each other to press the region to be sealed along a transverse direction to the direction of vertical motion of the tubular wrapper. Because of the movement of the bars, the tubular wrapper is braked intermittently, causing considerable damage to the seal region. During the motion of the wrapper, the bars slide on the wrapper causing incorrect seals and the damage to the sealed area.
The prior art discloses devices able to overcome the aforementioned problems by providing bars movable along the path of the tubular wrapper.
As is described for example in European patent EP1125847, the forming device provided with movable bars is constituted by two adjacent support frames having respective belts movable along a closed path. The tubular wrapper is actuated through the belts, at a rectilinear segment of the closed path, parallel to the direction of actuation of the wrapper. Each belt bears a plurality of carriages which are movable along the path. Each carriage bears a heated bar adapted to abut on the surface to be heated of the tubular wrapper. In this situation, when the carriages are positioned at the rectilinear segment, the bars of each pair of carriages abut against each other pressing the region to be sealed of the tubular wrapper. The pressing operation is then performed while each pair of carriages is maintained in motion along the direction of actuation of the tubular wrapper. The device described above has important drawbacks, although it solves the problem of avoiding any relative sliding between the bars and the wrapper.
These drawbacks are linked mainly to the structural complexity of the sealing device and of the overall size presented thereby. It should be noted that the structure constituted by two frames, each of which has a belt, is very bulky, further considering that each belt has respective motion transmission member. Moreover, it should be considered that each pair of carriages must necessarily be in synchrony during the sealing operation to make the pressing between one bar and the other efficient. To maintain the correct positioning of the carriages, electronic means are provided for controlling and adjusting. Such means are sometimes highly complex and have an excessive cost of construction. Consequently, the presence of means for controlling and adjusting the belts causes high costs for the production and/or commercialisation of the known devices.